FIG. 1A-1C are illustrations of solar tower systems for generating solar steam. The system includes a solar tower 50 which receives reflected focused sunlight from a plurality 60 of heliostats. Mounted on the solar tower 50 is a solar steam system 500 including one or more solar receivers. Each solar receiver is configured to heat water and/or steam and/or supercritical steam using insolation received from the heliostats. In different examples, solar tower 50 may be at least 25 meters, at least 50 meters, at least 75 meters, or even higher.
In the example of FIG. 1A, the solar steam system solar steam system 500 is mounted at or near the top of tower 50. In the example of FIG. 1B, secondary reflector 40 is mounted at or near the top of tower 50. In the example of FIG. 1B, secondary reflector 40 receiver insolation from the heliostats 60 and reflects the insolation downward to solar steam system 500 including the receivers.
In the example of FIG. 1C, there are multiple (i.e. two or more than two) solar towers 50, each tower being associated with a respective solar steam system 500. At any given time, a given heliostat may be directed to a solar receiver of any one of the towers. Throughout the figures, “INS” is an abbreviation for ‘insolation.’
FIG. 2A is a block diagram of a solar steam system including (i) a solar steam superheater 820; (ii) steam turbine 580 and (iii) upstream and downstream conduit assemblies 202 and 206 (for example, pipe assemblies comprising one or more pipes). The direction of flow (in this schematic diagram, from left to right) is indicated by a block arrow.
Pressurized steam (e.g. saturated pressurized steam or supercritical steam) (i) first enters solar superheater 820 from ‘upstream’ conduit assembly 202, (ii) subsequently traverses steam solar superheater 820 where the pressurized steam is subjected to insolation and superheated from temperature TINLET to temperature TOUTLET (also referred to TSHINLET and TSHOUTLET as where ‘SH’ is an abbreviation for the solar superheater); and (iii) subsequently flows from the outlet of the solar superheater to steam turbine 580 via downstream conduit assembly 206.
One salient feature of the system of FIG. 2A is that (i) steam is heated within steam superheater 820 from temperature TSHINLET to temperature TSHOUTLET (e.g. typically, TSHOUTLET−TSHINLET is a ‘significant’ or ‘substantial’ temperature difference—for example, at least 50 degrees Celsius or at least 100 degrees Celsius) which is not insulated on at least one major surface; and (ii) steam flows within conduit assemblies 202, 206 preferably at a substantially constant temperature, for example, due to the insulation (for example, insulation around a pipe such as a metal pipe).
Within steam turbine 580, the pressurized superheated steam drives turbine 580 to generate useful work. In the present document, ‘ST’ is used as an abbreviation for steam turbine. ‘SH’ is used as an abbreviation for ‘super heater.’
Typically, steam turbine 580 is operatively linked to a dynamo (not shown) in order to generate electricity—for example, as part of a solar thermal power plant. In order for steam turbine 580 to operate, steam must be supplied at a minimum temperature, referred to herein as TSTMINIMUM or TSTMIN. In the event that the ‘colder’ steam whose temperature is below minimum temperature TSTMIN enters turbine 580, turbine 580 is liable to undergo an ‘uncontrolled shutdown’ which may be damaging for turbine 580 and/or which may result in a situation where turbine 580 may be subsequently started up again only after paying some sort of ‘thermodynamic price’ and an associated longer startup time.
For this reason, flow parameters of the solar thermal system and/or insolation parameters (for example, describing a flux density or distribution on solar steam superheater SH 820) are regulated so that pressurized steam within solar superheater SH 820 is sufficiently heated to that a temperature of outlet steam TSHOUTLET exceeds the minimum turbine operating temperature TSTMIN.
As noted above, typically the difference (TSHOUTLET−TSHINLET) is a ‘significant’ or ‘substantial’ temperature difference—therefore, the insolation control system and/or flow parameters are arranged so a flux density on solar superheater SH 820 is sufficiently strong and so that pressurized steam is resident within solar superheater SH 820 for sufficient time so that while within superheater 820, the pressurized steam ‘crosses the minimum operating temperature threshold of turbine 580.’ When steam ‘crosses the minimum temperature of turbine 580,’ it is heated from a temperature below TTURBMIN.
This is illustrated in FIG. 2B which illustrates a temperature profile of the pressurized steam on its journey to steam turbine 580 via conduit assemblies 202, 206 and solar steam superheater 820. As illustrated in FIG. 2B, the temperature of the pressurized steam increases (often dramatically) within steam superheater 820, while within the conduit assemblies 202, 206 there is little or no change of temperature. Thus, in FIG. 2B even if a certain small amount of heat is lost to the environment within conduit assembly 206, pressurized steam is heated with steam superheater SH 820 to such an extent that both TSHOUTLET (i.e. the temperature at the outlet of steam superheater SH 820) and TSTINLET (i.e. the temperature at the inlet of steam turbine 580) exceed TTURBMIN.
FIG. 2C illustrates one example where steam superheater SH 820 is located at or near the top of solar tower 50 and where steam turbine 580 is located at or near ground level. In this example, downstream conduit assembly 206 is and/or includes an elongated insulated pipe.
Insolation is variable both predictably (diurnal variation) and unpredictably, due to cloud cover, dust, solar eclipses, or other reasons. FIG. 3 illustrates an example of the intensity of beam normal insolation as a function of hour of the day, over the course of a clear-sky day. As is illustrated within the dotted rectangle, around the time of sunset, the intensity of insolation drops steeply and rapidly.